The first set of the match played in humid conditions hinged on a Machac service game at 3-3 where the unseeded Czech's forehand missed its target on break point to give Sinner a 4-3 lead.
The Italian would wrap up the set with a love hold when Machac was unable to put a second serve back in play.
In the second set, Machac's forehand sailed long to give Sinner the break and a 2-1 lead. Sinner would break again with a backhand winner for 4-1 and closed out the contest with a serve out wide that Machac could not get back.
Sinner, who was a finalist at the tournament in 2021 and 2023, produced 16 winners to four unforced errors in a stress-free victory.
The win was Australian Open champion Sinner's 20th of the year and sets up a potential rematch with Medvedev in the semis after the pair met in last year's Miami Open final and January's Melbourne Park final.
Sinner has lost just one match this year, falling in the semi-finals of Indian Wells to eventual champion Carlos Alcaraz (20).
